A little over 2000 years ago, the world of Ocean was torn apart and nearly destroyed by a great Cataclysm.
Prior to the event, the world was very different. Large continents covered in verdant forests and rolling plains, separated by deep oceans. Great and ancient empires and cosmopolitan city-states gathered wealth and power and culture.
The the Cataclysm happened. No one is sure what it was, or where it came from. Some scholars believe it was a threat from beyond the stars, others believe it was the work of Tzatzimime, while others believe the cause could have been the work of mages dabbling in forces beyond their control. Whatever the cause, the effect was nearly the end of the world. The only entities that had both the knowledge and power to stand against the threat were the gods of the Elves. They held back the worst of the Cataclysm, sacrificing themselves to save what they could of the world.
Ocean was rended by quakes and fire, and most of the surface crumbled and collapsed into the Underdark, the seas rushing in to cover the ruin as the Northern ice cap melted. A handful of population centers survived but untold billions of souls perished in the disaster. The psychic backlash of the deaths of so many mortals and gods ripped through the minds of the survivors blasting their consciousness and leaving nothing but splinters of shattered memory of the time before the destruction.
When the dust settled and the shaking stopped, Ocean had been irrevocably changed. Life goes on, however, and the survivors set about rebuilding their lives and societies based on the fragments of memory left to them.